Adhesives may be used to bond parts and structures in a wide variety of applications. In the aircraft industry, for example, adhesives may be used to bond patches to a structure such as a skin panel in order to improve, rework and/or repair an area of the structure. In some cases, the patch and/or the structure may be formed of composite materials. After applying a layer of adhesive to the structure and/or the patch, pressure along with heat is applied to the patch in order to cure the adhesive and form a strong bond at the patch and structure. This bonding process is not easily performed in the field, and may therefore be normally carried out under controlled conditions such as, without limitation, within a maintenance/repair hanger facility where specialized handling equipment and skilled technicians with knowledge of composites are available.
The strength and/or longevity of a bonded patch may depend in part on the thickness of the adhesive, the evenness of the adhesive thickness over the area of the patch and/or the presence of voids or air pockets between the patch and the structure caused by, without limitation, porosity in the bond. Bond line thickness and porosity may be controlled to some degree by controlling the pressure that is applied to the patch during its installation. However, determining the exact pressure necessary to achieve a particular bond line thickness maybe difficult, and in any event, applying this exact pressure uniformly across the patch may be challenging. Film type adhesives of constant thickness represent one possible solution to the problems discussed above, however the use of film adhesives may not be practical in some applications because of the special handling that they may require, such as, without limitation, the need to refrigerate the film until it is ready for use.
Accordingly, there is a need for a method of bonding a patch to a structure that allows close control of bond line thickness over substantially the entire area of the patch, and which reduces or eliminates porosity in the bond due to voids. There is also a need for a method of bonding patches to structures that may be carried out in the field, using an adhesive that does not require special handling, is not highly dependent on an installer's skill and which yields consistent, repeatable results.